On Wed, Sep 17, 2014 at 2:06 PM, Sam mite <[email protected]> wrote:
> Hi, I am trying the CMA equalizer of gnuradio and for understanding I am > studying the reference paper mentioned in the doc as well. I have a > question after going through the code- Why the real and imag part of the > error signals are being clipped at 1. > > float re = gr::clip(error.real(), 1.0); float im = gr::clip(error.imag(), > 1.0); > Shouldn't it be "d_modulus" instead of 1. > > Regards, > > Sam > The answer is no. The clipping is just to make sure that the error signal doesn't walk away too far or go to some strange state if the incoming signal is too ugly. There's nothing that I can find that ties that value to the modulus at all, though I can see why you might think so. In fact, when you make the change you suggested, the results get noticeably worse. I've attached an example that uses our dynamic fading model to explore the results. You can select between different UMTS PDP models, both of which are pretty bad. I found that restricting this error value even more makes the algorithm a bit more robust, though it likely takes longer to lock. But when using d_modulus here, the algorithm never actually converges. Tom
digital_cma_equalizer_cc.grc
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